A chuck or collet actuating apparatus is known (German Patent Document DE-OS No. 31 17 850) which is part of a machine tool and which comprises a rotating clamping cylinder, an axially slidable clamping piston mounted in the clamping cylinder rotating with it and a coaxial cylindrical projecting portion in the clamping cylinder of a diameter smaller than the clamping piston diameter.
In this apparatus the clamping piston always performs the same axial clamping displacement even when a shorter clamping displacement would suffice as apparent from the clamping process.